Automobiles are propelled by tires, which are rotated by rotational drive power converted from drive power generated by an internal combustion engine supplied with fuel. Various attempts have been made recently to increase the fuel consumption rate (mileage) of internal combustion engines in such automobiles, since a reduction in the amount of consumed fuel makes the engines energy efficient and contributes to the environmental protection of the earth.
One of such attempts involves reducing the sliding resistance between sleeves in an internal combustion engine and the pistons that are reciprocally moved in the sleeves. Such reduced sliding resistance allows the piston to move back and forth more easily. Therefore, the drive force required for the piston to undergo reciprocating movement is reduced, thereby resulting in a reduction in the amount of consumed fuel.
Sliding resistance may be lowered by depositing a layer containing a highly lubricative substance on a sleeve or a piston skirt in order to increase the lubricating ability of the sleeve or the piston skirt. For example, according to Japanese Laid-Open Patent Publication No. 2009-068584, it has been proposed to provide a layer of binder resin with MoS2, C, or the like dispersed therein.
The applicant has further proposed, in Japanese Laid-Open Patent Publication No. 2003-013802, to form line marks on a piston skirt, and to grow over the surface of the line marks an anodic oxide coating, which is impregnated with a lubricant and a molybdenum disulfide coating successively in this order.